Conventional automotive vehicles typically include a mechanical brake pedal that is continuously connected to a brake lever or arm. The motion of the arm in turn actuates a braking mechanism, such as a disc brake and/or drum brake, to thereby slow or stop the vehicle. The rate of deceleration imparted to the vehicle depends largely on the amount of force applied to depress the brake pedal, as well as the travel position of the brake pedal within or along its fixed range of motion. Conventional hydraulic braking systems are powered by a supply of pressurized brake fluid from a master cylinder. Such a mechanical, fluid-driven braking system generally responds relatively quickly and accurately to the force applied to the brake pedal through its entire range of motion, providing what could be described as a “normal” or conventional brake pedal feel.
By contrast, an electronic or by-wire braking system is often used in electric vehicles, as well as in hybrid vehicles which are alternately and selectively powered by an internal combustion engine and one or more electric motor/generators. In an electronic braking system (EBS), the braking command or input applied as a force to a brake pedal by an operator is converted by an encoder device into an electrical signal. This electrical braking signal, also known as a braking torque request, is then transmitted or communicated to the point of application, wherein one or more actuators operate in response to the signal to slow or stop the vehicle. Braking torque may be applied directly using a conventional braking mechanism, or more commonly by applying an individual electronic braking unit positioned in proximity to each wheel, and/or to the transmission output member, thereby slowing the vehicle in a precisely controlled manner.
In an electric or hybrid vehicle, the brake pedal is isolated from the point of braking torque application, and therefore is attached to one or more pedal sensors which detect or measure the pressure on the brake pedal and convert the pressure into the transmittable electrical signal. The controller has preprogrammed braking system logic for translating the detected brake pedal measurements into corresponding braking torque requests. Typically, such braking logic includes an accessible braking torque lookup table containing specific braking torque requests corresponding to the various detected brake pedal forces.
However, certain pressure sensors may have less than optimal resolution, particularly under low force conditions. Using a brake pedal force sensor alone under these conditions may result in an error or variance in the braking torque request communicated to the electronic braking system when compared to the vehicle operator's intended braking force. While sensors used to measure a brake pedal's relative position within or along its range of motion, i.e., the brake pedal travel position, generally have better resolution at these low pressure ranges, hysteresis within the braking system may also potentially lead to errors or variances in the resulting applied braking torque request in the event of an attempted direct or immediate switch to such a sensor during low pressure applications.